1. Field of the Invention
The present invention relates to a broadband orthogonal frequency multiplexing access system, and more particularly to a method for allocating burst data to a Mobile Subscriber Station (MSS).
2. Description of the Related Art
Conventional mobile communication networks were developed to provide a voice-based service, that is, voice communication. The mobile communication network has inherent disadvantages in that the data transmission bandwidth is relatively narrow since transmission of voice data only does not need much bandwidth, and service charges are expensive. Recently, however, with the rise in demand for wireless services, including Internet access and multimedia content, the conventional mobile communication networks cannot satisfy user demand. The Institute of Electrical and Electronics Engineers (IEEE) 802.16e standardization group of the IEEE, an international standardization organization, is lobbying for the adoption of IEEE 802.16d as the standard for providing wireless broadband Internet service to fixed subscriber stations.
As compared with a conventional wireless technology, the IEEE 802.16d standard allows mass storage data to be transmitted in a short time by providing a wide bandwidth for data and allows channels to be used efficiently by sharing the channels by all users. However, in the IEEE 802.16d standard, all users connected to a base station share, and use, the common channel. Further, since a use interval of the channel by each user is allocated by the base station, the base station must inform each user of a MAP representing burst allocation information, so that each user can share and use the channel each frame. In the IEEE 802.16d standard, the MAP is classified into the UL_MAP and the DL_MAP, which are contained in front portions of each frame, and then transmitted to all users.
FIG. 1 is a diagram showing the frame structures of a downlink and an uplink in the IEEE 802.16d according to the prior art. Referring to FIG. 1, a vertical axis represents multiple subchannel numbers 147 and a horizontal axis represents Orthogonal Frequency Division Multiplexing Access (OFDMA) symbol numbers 145.
First, the downlink 149 will be described. A preamble 111 is located at a front portion of the subchannel constituting the downlink. Broadcast data information, such as a Frame Control Header (FCH) 113, a DL_MAP 115 and an UL_MAP 117 is located behind the preamble 111. Further, DL bursts 121, 123, 125, 127 and 129 are located behind the broadcast data information.
Next, in the uplink 153, preambles 131, 133 and 135 exist at a front portion of UL bursts 137, 139, and 141, respectively, with a ranging subchannel 143.
The DL_MAP 115 and the UL_MAP 117 include information regarding positions and allocation of the DL bursts 121, 123, 125, 127 and 129 and the UL bursts 137, 139 and 141. The information is transmitted from a base station to an MSS. Then, the MSS variably receives a subchannel with a combined frequency and symbol for each frame by means of the position and the allocation information of the UL bursts 137, 139 and 141 and the DL bursts 121, 123, 125, 127 and 129 contained in the DL_MAP 115 and the UL_MAP 117. The subchannel used in each frame is not fixed but variable.
Each MAP information element (MAP_IE) represents a MAP for one terminal. Each terminal checks whether a basic connection identifier (basic CID) contained in the MAP_IE is the basic CID of the terminal and transmits/receives bursts through the subchannel on a frequency and symbol represented by a corresponding MAP_IE.
As described above, in the existing IEEE 802.16 broadband OFDMA system, the base station allocates the subchannel to the mobile terminal, which is to be used for transmitting the bursts to each terminal in a corresponding frame through the broadcast data information, such as the DL_MAP and the UL_MAP. However, the base station must transmit burst allocation information to each terminal. The allocation information itself according to the transmission imposes a large overhead on the system. In particular, when a plurality of terminals are connected to the base station, the burst allocation information degrades system performance because the burst allocation information uses more resources of the shared transmission channel.